The present invention generally pertains to control systems and is specifically directed to improvements in control systems for plants that typically are operated in a closed-loop manner.
A "plant" is defined as a physical operating unit or system. In closed-loop systems the operation of the plant is controlled by a control signal f(s) which is derived in accordance with a control function based upon a measured response of the plant. In some prior art closed-loop control systems, a model of the plant is simulated in a closed-loop control system on a continuous basis and the response of the model is compared with the response of the actual plant to effect corrections.
A physical system is characterized by system state variables. For example, a missle airframe comprises a system where missile spatial attitude is one state variable and the tail actuators and aerodynamic panels providing the necessary forces acting upon the airframe are other state variables. The system may be represented mathematically via differential equations or in block diagram form, as in FIG. 1, where the blocks express the physical system via mathematical transformations, such as LaPlace transforms.
FIG. 1 shows an exemplary closed-loop linear control system for an airframe 10 having an operating characteristic G(s), which is controlled by a servo 11 having a constant gain characteristic (K). The servo 11 and airframe 10 constitute the "plant" in the system of FIG. 1.
In imposing control over the airframe 10, a sensor 12, such as a gyro, senses a state variable, such as the airframe attitude E.sub.o (s). The electrical output of the gyro E.sub.os (s) is then combined differentially with an electrical signal representing the desired attitude E.sub.i (s). The resulting difference, represented by an error signal e(s), is manipulated electrically in accordance with a shaping network 13 to yield a specific behavior as a function of time. The precise behavior is prescribed mathematically and implemented electrically as a control signal f(s). The "electrical" implementation is sometimes accomplished through use of a digital computer, wherein the shaping network 13 performs a control function g(s) defined by a control algorithm. The control signal f(s) represents the desired position of the tail panels which will result in aerodynamic forces which cause the airframe attitude E.sub.o (s) to achieve the desired airframe attitude E.sub.i (s).